Packetisation of data for communication/transmission of the data is well known. Many example packetisation algorithms and communication protocols/standards exist, such as the Realtime Transport Protocol, RTP, (for more details, see http://www.rfc-editor.org/rfc/rfc3550.txt). These packetisation methods shall not be described in detail herein.
Generally speaking, though, the data that is to be communicated (transmitted) is divided into one or more blocks of data. Each block is communicated as a separate data packet. Various additional data is added to each block of data to form the corresponding data packet. This additional data may be supplied within a header of the data packet. The additional data may include an error correction and/or detection code, a sequence number and a time associated with the data packet and/or its data (represented as a timestamp). The error correction and/or detection code helps determine whether a data packet that has been received at a receiver has any errors or is error-free. If an error-correction code is used, it may be possible to correct any detected errors to obtain an error-free data packet. The sequence number enables a receiver to order received data packets into the order in which the data packets were originally transmitted (it being possible that the data packets are received out of order). The timestamp may provide an indication of the time at which the corresponding data packet was sent or of the time to which the data of that data packet corresponds (for example, the timestamp may represent the time at which the data of that data packet was originally captured, i.e. the moment when the data was sampled in order to be encoded).
There are many applications in which it is desirable to have an estimate of a frequency associated with the data packets. This frequency could be the frequency at which the data packets are transmitted. Alternatively, this frequency could relate to a frequency of the data contained within the data packets (such as a video frame-rate for data packets containing video data or an audio sampling-rate for data packets containing audio data). This estimate of the frequency is useful for applications such as video frame-rate detection, video frame-rate conversion (temporal transcoding), motion analysis, and audio up/down sampling.
However, currently proposed methods of determining an estimate of this frequency are not very accurate. In particular, it is desirable to have a method of estimating the frequency that still provides accurate estimates in situations in which (i) the timestamps for received data packets have constant increments; and/or (ii) some of the data packets are lost (or not received), thereby disrupting the sequence of received timestamps and their apparent relationship; and/or (iii) the timestamps for received data packets change in a non-standard or unexpected manner; and/or (iv) some of the data packets are not sent, i.e. the source of the data packets chooses to skip some data packets (e.g. one or more video frames may be dropped/omitted from the packet stream).